Loudspeaker using an electro-active device

Abstract

A loudspeaker comprising: a support, a sound-generating element mounted to the support for vibration to generate sound; and an electro-active device coupled between the support and the sound-generating element for vibrating the sound-generating element in response to an electrical signal. The electro-active device comprises a structure extending along a minor axis which extends in a curve around a major axis parallel to the vibration direction of the sound-generating element, the structure comprising successive electro-active portions arranged with electrodes to bend around the minor axis on activation in response to application of the electrical signal to the electrodes, and coupled together such that bending of successive portions causes concomitant rotation of adjacent portions around the minor axis adding incrementally along the minor axis, which rotation causes concomitant change of the axial length of the structure along the major axis.

The invention claimed is: 
     
       1. A loudspeaker, comprising:
 a support; 
 a sound-generating element mounted relative to the support for vibration in a vibration direction to generate sound; and 
 an electro-active device coupled to the sound-generating element for vibrating the sound-generating element in response to an electrical signal, the electro-active device comprising a continuous electro-active member having two ends between which ends the member extends along, and curves in a helix around, a minor axis, which minor axis extends in a curve around a major axis parallel to the vibration direction of the sound-generating element, the continuous electro-active member being arranged with electrodes to bend around the minor axis on activation in response to application of the electrical signal to the electrodes, and coupled together such that bending of the continuous electro-active member causes concomitant rotation of the continuous electro-active member around the minor axis adding incrementally along the minor axis, which rotation causes concomitant relative displacement of the two ends of the continuous electro-active member along the major axis. 
 
     
     
       2. A loudspeaker as claimed in  claim 1 , wherein the curve along which the minor axis extends is planar. 
     
     
       3. A loudspeaker as claimed in  claim 2 , wherein the curve along which the minor axis extends subtends less than 360E at the major axis. 
     
     
       4. A loudspeaker as claimed in  claim 2 , wherein the curve along which the minor axis extends is a planar spiral. 
     
     
       5. A loudspeaker as claimed in  claim 2 , wherein the support comprises a casing having a recess covered by the sound-generating element, the electro-active device being arranged in the recess. 
     
     
       6. A loudspeaker as claimed in  claim 5 , wherein the sound-generating element is planar and extends parallel to the curve along which the minor axis extends. 
     
     
       7. A loudspeaker as claimed in  claim 5 , wherein the casing has a base wall and peripheral side walls defining the recess. 
     
     
       8. A loudspeaker as claimed in  claim 5 , wherein the electro-active device is coupled to the sound-generating element by a mount providing clearance therebetween. 
     
     
       9. A loudspeaker as claimed in  claim 7 , wherein the base wall of the casing is planar and the electro-active device is coupled to the base wall of the casing by a mount providing clearance between the base wall and the electro-active device. 
     
     
       10. A loudspeaker as claimed in  claim 1 , wherein the electro-active device is positioned in front of the sound-generating element and is coupled to the support by a frame which is sufficiently open to allow passage of sound generated by the sound-generating element. 
     
     
       11. A loudspeaker as claimed in  claim 10 , wherein the sound-generating element is a cone defining a recess and the electro-active device is at least partially within the recess. 
     
     
       12. A loudspeaker as claimed in  claim 11 , wherein the frame comprises a plurality of arms extending from the support to the electro-active device. 
     
     
       13. A loudspeaker as claimed in  claim 10 , wherein the frame comprises a plurality of arms extending from the support to the electro-active device. 
     
     
       14. A loudspeaker as claimed in  claim 10 , wherein the support comprises an annular member to which the periphery of the sound-generating member is mounted and from which the frame extends. 
     
     
       15. A loudspeaker as claimed in  claim 1 , wherein the sound-generating element is mounted to the support by a bearing. 
     
     
       16. A loudspeaker as claimed in  claim 15 , wherein the bearing comprises a resiliently-deformable toroidal member surrounding the sound-generating element. 
     
     
       17. A loudspeaker as claimed in  claim 16 , wherein the toroidal member is formed from a resiliently-deformable material. 
     
     
       18. A loudspeaker as claimed in  claim 16 , wherein the toroidal member is a flexible hollow envelope containing a resiliently-deformable material. 
     
     
       19. A loudspeaker as claimed in  claim 15 , wherein the bearing comprises a plurality of resiliently-bendable flexure strips spaced around the sound-generating element and aligned with the direction of vibration of the sound-generating element, each flexure strip being bent over with the same face of the flexure strip contacting the sound-generating element and the support. 
     
     
       20. A loudspeaker as claimed in  claim 19 , wherein each flexure strip is arranged in a loop. 
     
     
       21. A loudspeaker as claimed in  claim 19 , wherein the flexure strips are arranged in aligned pairs facing opposite directions. 
     
     
       22. A loudspeaker as claimed in  claim 1 , wherein the sound-generating element is mounted to the support by a plurality of flexures, each flexure comprising a pair of resilient strips facing the direction of vibration of the sound-generating element with one end of each strip being coupled together and the other end of the strips being coupled to the support and the sound-generating element, respectively. 
     
     
       23. A loudspeaker as claimed in  claim 1 , wherein the electro-active device is coupled to the sound-generating element by an elongate rod. 
     
     
       24. A loudspeaker as claimed in  claim 23 , wherein the curve along which the minor axis extends is a helix, the electro-active device is connected to the support at a first end of said continuous electro-active member proximal to the sound-generating element and to the elongate rod at the second end of said continuous electro-active member distal from the sound-generating element, the rod extending through the structure. 
     
     
       25. A loudspeaker as claimed in  claim 1 , wherein the sound generating member is a display. 
     
     
       26. A loudspeaker as claimed in  claim 25 , wherein the display is a liquid crystal display. 
     
     
       27. A loudspeaker as claimed in  claim 1 , wherein the minor axis extends in a curve which is one of: a helix; a spiral; a series of at least two coaxial spirals; a series of at least two coaxial helices; a circle; or an arc of a circle. 
     
     
       28. A loudspeaker as claimed in  claim 1 , wherein the minor axis subtends less than 360E at the major axis. 
     
     
       29. A loudspeaker as claimed in  claim 1 , wherein
 the continuous electro-active member includes piezoelectric material; and 
 the piezoelectric material is a piezoelectric ceramic or a piezoelectric polymer. 
 
     
     
       30. A loudspeaker as claimed in  claim 1 , wherein
 the continuous electro-active member includes piezoelectric material; and 
 the piezoelectric material is lead zirconate titanate (PZT) or polyvinylidenefluoride (PVDF). 
 
     
     
       31. A loudspeaker as claimed in  claim 1 , wherein the continuous electro-active member has a plurality of layers including at least one layer of electro-active material. 
     
     
       32. A loudspeaker as claimed in  claim 31 , wherein the continuous electro-active member has at least two layers of electro-active material to act as a bimorph or multimorph. 
     
     
       33. A loudspeaker as claimed in  claim 32 , wherein the continuous electro-active member has at least one sensor layer with associated electrodes in addition to the electrodes associated with said electro-active material. 
     
     
       34. A loudspeaker as claimed in  claim 31 , wherein the continuous electro-active member has at least one sensor layer with associated electrodes in addition to the electrodes associated with said electro-active material. 
     
     
       35. A loudspeaker as claimed in  claim 31 , wherein the continuous electro-active member is oriented with the layers across the width of the member extending parallel to the minor axis. 
     
     
       36. A loudspeaker as claimed in  claim 1 , wherein the continuous electro-active member has a variation along the length of the minor axis to vary the degree of bending. 
     
     
       37. A loudspeaker as claimed in  claim 1 , wherein the continuous electro-active member is provided with external polymeric or elastomeric material. 
     
     
       38. The loudspeaker as claimed in  claim 1  provided as part of an array of loudspeakers, the plurality of which include a support, a sound-generating element mounted relative to the support for vibration in a vibration direction to generate sound, and an electro-active device coupled to the sound-generating element for vibrating the sound-generating element in response to an electrical signal and each comprising a continuous electro-active member having two ends between which ends the member extends along, and curves in a helix around, a minor axis, which minor axis extends in a curve around a major axis parallel to the vibration direction of the sound-generating element, the continuous electro-active member being arranged with electrodes to bend around the minor axis on activation in response to application of the electrical signal to the electrodes, and coupled together such that bending of the continuous electro-active member causes concomitant rotation of the continuous electro-active member around the minor axis adding incrementally along the minor axis, which rotation causes concomitant relative displacement of the two ends of the continuous electro-active member along the major axis.